Perfluoroalkyl sulfonic acid polymer electrolytes have been conventionally primarily used as proton conductive polymer electrolytes used for solid polymer fuel cells due to their excellent characteristics as fuel cells; however, this material is expensive.
In addition, although hydrogen and methanol are expected to take a prospective view as fuel used for fuel cells, a fuel cell by means of the above perfluoroalkyl sulfonic acid polymer and using methanol as fuel exhibits high permeability of the perfluoroalkyl sulfonic acid polymer to methanol, so the voltage and output are decreased.
In such situations, polymer electrolytes substituted for perfluoroalkyl sulfonic acid polymer materials, which are inexpensive and hardly permeate methanol, have been recently actively developed. Of these, materials having excellent heat resistance, in which a sulfonic acid group is introduced into an aromatic polyether having a high film strength are taken as a prospective view and, for example, polymer electrolytes of sulfonated polyether ketones (National Publication of International Patent Application No. 11-502249), sulfonated polyether sulfones (Japanese Patent Laid-Open Nos. 10-45913 and 10-21943) are proposed.
In addition, although polymer electrolytes crosslinked by radiation are recently disclosed from the viewpoints of permeation restraint of methanol and water resistance improvement (Japanese Patent Application Laid-Open No. 2004-269599), large-scale facilities are required for crosslinking by radiation and a membrane suffers from deterioration by radiation.
Furthermore, although a method is proposed that carries out amidation by use of an amine component for crosslinking (Japanese Patent Application Laid-Open No. 6-93114), an equivalent of a group attributable to proton conduction is decreased and the group is readily subjected to hydrolysis.